Just before Marilyn Monroe became a household name and starred in Gentlemen Prefer Blondes, Philippe Halsman photographed her for LIFE magazine and captured a few candid shots of her workout routine.

I absolutely adore this series – the fact that it took lifting weights to create that bombshell figure, the fact that she’s wearing jeans to workout in and the fact that she confesses to 10 minutes of ‘bust firming’ exercises every morning!